Add the possibility to "memoize values within the expectation block"

[jvenezia]

First of all thank you for this amazing Gem, it's a clean and simple solution to avoid n+1 regressions.

Could you explain why memoizing the action in rspec is not possible? Adding this ability would help a lot for the maintainability of our tests. Typically we always add the controller action in a let(:request) { get :action }, so this gem makes us write an exception.

[palkan]

Typically we always add the controller action in a let(:request) { get :action }, so this gem makes us write an exception.

Yeah, I experience the same :(

Could you explain why memoizing the action in rspec is not possible?

To detect N+1, we run the expectation block twice (even though you write it once). If we put get :action into a let definition, it only executes one. That is, when you write:

expect { request }.to perform_constant_number_of_queries

It unwraps into:

run_a = track_queries { request }

# request is memoized, so nothing happens here
run_b = track_queries { request }

expect(run_a).to eq(run_b)

I've been thinking about the following solution:

initial_memoized_vars = rspec_memoized_vars
run_a = track_queries { request }

# reset let-s initialized within a block
(rspec_memoized_vars - initial_memoized_vars).each { |var| rspec_reset_let(var) }

# request is no longer memoized
run_b = track_queries { request }

expect(run_a).to eq(run_b)

The problem is that RSpec doesn't provide an API to manipulate the memoization store. It could be hacked, of course. Maybe, we should think about it.